1. Field of the Invention
The present invention relates, generally, to an oil-free viscoelastic elastomer gel, which may be shaped and molded for being beneficially applied to a person's skin.
More particularly, the present invention relates to a composite article comprising a thermoplastic, heat-formable, and heat reversible, gelatinous elastomer composition, which is formed into a composite by heating with at least one substrate material, which may be applied to human skin. The elastomer composition is formed from one or more hydrogenated styrene/isoprene/butadiene block polymers and specialty esters and/or conventionally known compositions used to provide esthetic properties and emolliency to cosmetic formulations.
The composite articles of the invention, which include an oil-free thermoplastic, gelatinous elastomer composition, can be used to form viscoelastic elastomer-based gels that are well-suited for topical application (e.g., being appropriately moldable and formable into a variety of shapes and conformations.)
2. Description of the Prior Art
The prior art discloses a large number of compositions comprised of oil-extended thermoplastic block copolymers. Such teachings are to be found in U.S. Pat. Nos. 4,369,284; 4,618,213; 5,153,254; 5,633,286; 6,148,830; and 6,552,109, with the compositions disclosed therein generally including certain low viscosity triblock copolymers which have been plasticized with high levels of oil.
The inherent properties of the gelatinous elastomer compositions and articles made therefrom are many, with the gel compositions taught by the enumerated patents above exhibiting high dimensional stability, crack, tear, craze and creep resistance, excellent tensile strength and high elongation, long-service life under stress and capability of repeated handling, excellent processing ability for cast molding, are non-toxic, nearly tasteless and odorless, extremely soft and strong, highly flexible and possessing elastic memory, substantially with little or no plasticizer bleed out.
The oil plasticizers utilized by the prior art, which are generally present at levels significantly higher than the polymers themselves (typically about 3- to 15-times higher), serve a major role. The plasticized gels resist tearing under tensile loads or dynamic deformation, unlike unplasticized triblock copolymer gels, such as styrene-ethylene-butylene-styrene (“SEBS”) and styrene-ethylene-propylene-stryene (“SEPS”) gels, which possess high tensile strength, but will catastrophically snap apart into two reflective clean smooth surfaces when cut or notched under tensile or dynamic loads. A plasticized gel can be stretched by a first tensile load with uniform deformation to a measured length, and upon the application of higher tensile loads, the gel can be further extended without breaking. Upon release, the gel returns immediately to its original shape and any necking quickly disappears.
The nature of the oil plasticizers that are used in these products limits the application of these gels in a number of personal care, topical skin products. Examples of representative commercially available plasticizing oils include polybutenes, hydrogenated polybutenes, polybutenes with epoxide functionality at one end of the polybutene polymer, liquid poly(ethylene/butylene), liquid heterotelechelic polymers of poly(ethylene/butylene/styrene) with epoxidized polyisoprene, and poly(ethylene/butylene) with epoxidized polyisoprene. Also cited as appropriate examples of various commercially oils are ARCO PRIME, DURAPRIME and TUFFLO (trademarks) oils, and other white mineral oils, such as the BAYOL (trademark) series. The oily nature of these materials can often make them unsuitable for use of the gels for cosmetic application and topical medical delivery systems.
As used in this disclosure, the linear triblock co-polymers poly(styrene-ethylene-ethylene-propylene-styrene) is denoted by the abbreviation “SEEPS”; poly(styrene-ethylene-butylene-styrene) is denoted by the abbreviation “SEBS”; poly(styrene-ethylene-propylene-styrene) is denoted by the abbreviation “SEPS”; the branched copolymers poly(styrene-ethylene-propylene) is denoted by the abbreviation “SEP”; and poly(styrene-ethylene-butylene) is denoted by the abbreviation “SEB.”
The present invention is the result of efforts to develop a way for modifying the rigidity of these triblock copolymers, such as SEBS and SEPS gels, so as to provide a similar type of viscoelasticity in gels that are more readily applicable to personal care products in the cosmetic and medical delivery fields.